Boron is a chemical element with the symbol B and atomic number 5. Produced entirely by cosmic ray spallation and supernovae and not by stellar nucleosynthesis, it is a low-abundance element in the Solar System and in the Earth's crust. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. The largest known boron deposits are in Turkey, the largest producer of boron minerals. Elemental boron is a metalloid that is found in small amounts in meteoroids but chemically uncombined boron is not otherwise found naturally on Earth. Industrially, very pure boron is produced with difficulty because of refractory contamination by carbon or other elements.
Borax, its mineral form then known as tincal, glazes were used in China from AD 300, and some crude borax reached the West, where the alchemist Jabir Hayyan apparently mentioned it in AD 700.
Nearly all boron ore extracted from the Earth is destined for refinement into boric acid and sodium tetraborate pentahydrate. 70% of the boron is used for the production of glass and ceramics. The major global industrial-scale use of boron compounds is in production of glass fiber for boron-containing insulating and structural fiberglasses, especially in Asia. Boron is added to the glass as borax pentahydrate or boron oxide, to influence the strength or fluxing qualities of the glass fibers.
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